The present technique relates generally to monitoring blood pressure using an oscillometric technique. More specifically, the present technique relates to improving the performance of an oscillometric blood pressure estimation in the presence of arrhythmias, such as premature ventricular complexes (PVC's).
The oscillometric method of measuring blood pressure typically involves applying an inflatable cuff around an extremity of a patient's body, such as the patient's upper arm. The cuff is then inflated to a pressure above the patient's systolic pressure and then incrementally reduced in a series of small steps. A pressure sensor measures the cuff pressure at each step. The sensitivity of the sensor is such that pressure fluctuations within the artery resulting from the beating of the patient's heart may be detected. In particular, the pulses are transferred to the inflated cuff causing slight pressure variations within the cuff, which are detected by the pressure sensor in the monitor. The pressure sensor produces an electrical signal based on the measured cuff pressure. The electrical signal comprises a DC component, representing the constant cuff pressure at the pressure step, and a series of small periodic components, representing the pressure variations attributable to the beating of the patient's heart. These small periodic components are often referred to as “oscillation complexes” or simply “oscillations”.
A patient's blood pressure may be estimated based on an analysis of these oscillation complexes. After filtering out the DC component and amplifying the signal generated by the cuff pressure sensor, peaks may be determined for each oscillometric complex. At each decreasing pressure step, the peaks will tend to increase until a maximum amplitude is reached. Once this maximum amplitude has been reached, the peaks will begin to decrease with each decreasing pressure step. This maximum amplitude has been found to be representative of the patient's mean arterial pressure. The systolic and/or diastolic pressures can be derived either as the cuff pressures at which the oscillation amplitude is a predetermined fraction of the maximum amplitude, or by estimation techniques using direct processing of the oscillation complexes.
To improve accuracy and allow artifact rejection consecutive peak matching has been employed. Using this peak matching technique, oscillometric complexes at a given pressure step must have amplitude and pulse period characteristics that match within predetermined thresholds. Failure of two complexes to match may result in additional measurements being taken at the pressure step until two or more consecutive peaks are obtained which do match. In the presence of arrhythmias, such as PVC's, or noise, consecutive peak matching can prolong or prevent blood pressure determination, depending on the length of time needed to obtain consecutive matching peaks. Matching of non-consecutive peaks may also be employed but may be complicated by the difficulties associated with matching pulse periods. In addition, PVC's and other arrhythmias alter peak amplitudes in addition to pulse periods, further complicating the process of obtaining matches. Therefore, a need exists for a technique allowing the rapid and accurate measurement of blood pressure in a non-invasive manner in the presence of arrhythmias, such as PVC's.